The subject matter of the present invention relates to automatic transmissions for motor vehicles. More specifically, it relates to an improved throttle valve system for an automatic transmission which is specifically designed to eliminate sticking of the valve as it reciprocates in its bore.
Generally speaking, automatic transmissions for motor vehicles include various gear arrangements with appropriate clutch plates and bands responsive to hydraulic oil pressure to effect shifting of the gears in response to the speed of the vehicle. A valve body and casing form the basic elements of the automatic transmission. The valve body and casing contain various inter-related passages, valves, springs and orifices such that the valve body receives signals in the form of hydraulic pressures which route transmission oil through appropriate passages in the casing to clutch plates and bands to automatically effect sequential shifting of gears. The valve body itself cooperates with a separator plate disposed between the valve body and the casing. The separator plate includes orifices and openings of different size which communicate with inter-related passages in the valve body and casing to route oil through the transmission and ultimately effect gear shifting. For a fuller discussion of the valve body, and separator plate, and the manner in which these elements cooperate in an automatic transmission, attention is respectifully directed to U.S. Pat. No. 4,449,426 issued to the present applicant on May 22, 1984.
An essential component of the valve body of an automatic transmission is the throttle valve system. As is well known in the art, the throttle valve of an automatic transmission regulates the flow of transmission oil through the valve body. More specifically, the throttle valve reciprocates in a bore or sleeve, and the position of the throttle valve is controlled by the depression of the accelerator pedal of a motor vehicle through an appropriate linkage system. The throttle valve may be moved between a first zero or low throttle position and a second high or full throttle position. The position of the throttle valve in the bore regulates the flow of transmission oil by blocking or permitting fluid flow through different openings defined in the bore. The basic operation of the throttle valve is well known to those skilled in the art.
One major cause of automatic transmission failure results from the sticking of the throttle valve in its bore. If the throttle valve becomes stuck in the bore and fails to reciprocate in relation to accelerator pedal depression, the transmission system receives an inaccurate pressure signal resulting in slippage and clutch and band failure. Sticking of the throttle valve is most commonly caused by particles or other contaminents introduced into the system and circulated by the transmision oil itself. Any particles or other matter having a largest dimension greater than the clearance provided between the periphery of the throttle valve and its bore may potentially become wedged therebetween. Such wedging is the principal cause for the sticking of the throttle valve and thus is a significant factor in automatic transmission failure.
It is an object of the present invention to overcome the problem of sticking of throttle valves by providing an improved throttle valve system capable of shearing particles which may become wedged to a size in which they no longer are capable of wedging between the valve and its bore.
It is a further object of the invention to provide an improved throttle valve system which provides positive additional force applied to the throttle valve only at such times when that valve is stuck.
It is a further object of the invention to provide an improved throttle valve system which alerts a driver with a positive physical indication when the valve becomes stuck.
Other objects and advantages of the improved throttle valve system will become apparent in the following discussion of the improved system.